The present invention relates to a cleaning apparatus and a cleaning method. More particularly, the present invention relates to a cleaning apparatus and cleaning method suitable for cleaning of substrates requiring a high degree of cleanliness, such as semiconductor substrates, glass substrates, and liquid crystal panels.
With the progress of the technology to fabricate high-integration semiconductor devices in recent years, circuit wiring patterns or interconnections on semiconductor substrates have been becoming small and fine, and distances between wiring patterns have also been decreasing. In the processing of semiconductor substrates, such particles as fine semiconductor particles, dust particles, and crystalline protrusions may adhere to the substrate surface. If particles larger than the distances between wiring patterns remain on the substrate surface, problems such as short-circuiting between wiring patterns occur. Accordingly, particles that may be present on the substrate surface have to be satisfactorily smaller than the distances between wiring patterns. These circumstances also apply to the processing of glass substrates used for masks or the like and the processing of substrates such as liquid crystal panels. In compliance with these demands, a cleaning technique for removing even finer particles, i.e. submicron-level particles, from semiconductor substrates or the like is needed.
The semiconductor substrate is polished in order to make the substrate surface flat. There are publicly known methods of cleaning the polished semiconductor substrate. One of the known cleaning methods is scrub cleaning wherein a rotating substrate is supplied with a cleaning liquid, and while doing so, the substrate is rubbed with a cleaning member comprising a brush, a sponge or the like, thereby the substrate is cleaned. Another known cleaning method is spray cleaning wherein a cleaning liquid is sprayed toward a rotating substrate under the application of ultrasonic vibrational energy or high pressure. The substrate after the completion of the cleaning process is dried, for example, by spinning.
A conventional cleaning apparatus for performing the above-described cleaning process has a supporting device for supporting the substrate, a cleaning cup surrounds the periphery of the supporting device to prevent contamination of the outside of the cleaning cup, which might otherwise be caused by a cleaning liquid splashed by the centrifugal force induced by the rotation of the substrate. The cleaning apparatus further has a cleaning vessel covering the periphery of the cleaning cup.
When the substrate is cleaned by using two different kinds of chemical liquids, two units of cleaning apparatus, i.e. a primary cleaning apparatus and a secondary cleaning apparatus, are juxtaposed with each other. In the primary cleaning apparatus, cleaning using one chemical liquid is carried out. Thereafter, cleaning using the other chemical liquid is performed in the secondary cleaning apparatus. Next, rinsing using pure water is carried out in the secondary cleaning apparatus. Further, drying (e.g. spin drying) is performed in the secondary cleaning apparatus. Thereafter, the substrate is taken out of the secondary cleaning apparatus.
However, when the drying process for the substrate after the secondary cleaning process is carried out in the secondary cleaning apparatus, the substrate may be affected by reverse contamination. Here, the “reverse contamination” means that the cleaned semiconductor substrate is recontaminated with a by-product or the like. That is, when an alkaline chemical (e.g. NH4OH) is used for the chemical liquid cleaning in the primary cleaning apparatus and an acidic chemical (e.g. DHF) is used for the chemical liquid cleaning in the secondary cleaning apparatus, for example, the alkali attached to the substrate transferred into the secondary cleaning apparatus reacts with the newly supplied acid to form the by-product [e.g. NH4OH+HF→H2O+NH4F (by-product)]. The by-product adheres to and accumulates on the cleaning cup in the secondary cleaning apparatus and also to the interior of the cleaning vessel therein. The substrate in the secondary cleaning apparatus is rinsed with pure water subsequently. Therefore, the chemical liquids and the by-product are removed from the substrate. However, the by-product and the chemical liquids attached to and accumulated on the inner wall of the cleaning cup and the inner wall of the cleaning vessel, etc. remain attached thereto. Therefore, the remaining by-product and chemical liquids are whirled up by an air flow induced when the substrate is spin-dried, and adhere to the rinsed substrate. In this way, reverse contamination of the substrate occurs (i.e. defects increase).
The above-described problems may be solved by providing a drying apparatus independently in addition to the primary and secondary cleaning apparatuses to dry the rinsed substrate in the contamination-free drying apparatus. However, the use of this method leads to an increase in the installation area due to an increase in size of the system caused by the addition of another processing unit (i.e. a total of three processing units). In addition, the transfer control of the substrate between the three processing units becomes complicated, resulting in a reduction in the transfer throughput.